Variable displacement swash plate type compressor

ABSTRACT

A variable displacement swash plate type compressor comprises a suction chamber, a discharge chamber and a crank chamber. A flow rate control valve mechanism is provided along a refrigerant supply passage, which connects the discharge chamber to the crank chamber. The flow rate control valve mechanism is provided with a discharge pressure chamber and an intermediate chamber. A valve hole is provided between the discharge pressure chamber and the intermediate chamber, to permit both chambers to communicate with each other. A pressure sensitive member is provided in the intermediate chamber to separate the intermediate chamber into a first and a second pressure sensitive chambers. The first pressure sensitive chamber communicates with the discharge pressure chamber via the valve hole. The second pressure sensitive chamber communicates with either the crank chamber or the suction chamber. The pressure sensitive member is displaceable as a function of the pressure difference between the first and second pressure sensitive chambers. A restriction permits the first pressure sensitive chamber and the crank chamber to communicate with each other. A valve body is coupled to the pressure sensitive member to be displaceable in synchrony with the action of the pressure sensitive member, and regulates the opening of the valve hole according to the displacement. A return member biases the valve body and the pressure sensitive member to a valve open position when the pressure in the discharge chamber becomes almost zero.

BACKGROUND OF THE INVENTION

This application claims the priority of Japanese Patent ApplicationsNos. 3-238402 filed Sep. 18, 1991 and 4-110531 filed Apr. 28, 1992,which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to variable displacement swash plate typecompressors for use in vehicles and refrigerating systems. Moreparticularly, this invention relates to a compressor which controls thecrank chamber pressure. A volume control valve changes the inclinationof the swash plate, in relation to the difference between the pressuresin the compression chamber and the crank chamber, thereby controllingthe discharge volume.

DESCRIPTION OF THE RELATED ART

In conventional compressors of this type, as disclosed in, for example,Japanese Unexamined Patent Publication Nos. 60-175783 and 63-16177, ablow-by gas leaks from a compression chamber into a crank chamberthrough a side clearance between the outer surface of a piston and theinner wall of a cylinder bore during the compression process. The gaspressure in the crank chamber is controlled by properly discharging theblow-by gas to a suction chamber with the volume control valvemechanism. By regulating the gas pressure, it would be possible tovariably control the inclination of the swash plate or the dischargevolume of the compressor.

The above-mentioned supply of the blow-by gas from the compressionchamber into the crank chamber is not stable, particularly when thedischarge pressure is low. The blow-by gas alone provides insufficientamount of refrigerant supply to the crank chamber. It is therefore notpossible to promptly control the inclination of the swash plate, whichmay interfere with the proper variable control of the discharge volume.In an attempt to resolve this shortcoming, it has been proposed toprovide a refrigerant supply passage that connects the discharge chamberof the compressor and the crank chamber, and provides a restriction onthat passage to supply discharged gas according to the restricted amountinto the crank chamber, thereby compensating for the insufficient amountof refrigerant supply by the blow-by gas.

However, when the refrigerant supply passage with the restriction isprovided, as shown in FIG. 11, the amount of refrigerant supply throughthe refrigerant supply passage (indicated by a curve E3), and the amountof refrigerant supply by the blow-by gas (indicated by a curve E4)increase with an increase in the discharge pressure Pd. When thedischarge pressure Pd is particularly high, the sum of both amounts ofrefrigerant supply (indicated by the curve E3+4) becomes considerablylarge.

Such a variable displacement swash plate type compressor is often usedas a refrigerant gas compressor that forms a refrigerating circuitsystem in a refrigerating apparatus. When the discharge pressure Pd ishigh, the discharge gas, which exceeds the required level, is returnedfrom the discharge chamber to the suction chamber through therestriction disposed in the refrigerant supply passage, the crankchamber and the volume control valve mechanism. As a result, the ratioof the refrigerant gas to be supplied to the refrigerating circuitsystem of the refrigerating apparatus from the discharge chamber drops.This raises a new problem, that is a lower refrigerating performance.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a variabledisplacement swash plate type compressor which can smoothly effectvariable control of the discharge volume, and efficiently supply thecompressed gas without being affected by a change in the dischargepressure of the compressor.

To achieve the above object, the variable displacement swash plate typecompressor embodying the present invention comprises a suction chamberand a discharge chamber for a refrigerant gas, a plurality of pistonsreciprocate in respective cylinder bores, and a swash plate is disposedin a crank chamber. The pistons are drivably coupled to the swash plate.As each piston reciprocates, the refrigerant gas is sucked from thesuction chamber and compressed in the associated cylinder bore.

The refrigerant gas is then discharged into the discharge chamber. Theinclination of the swash plate is changed as a function of thedifference between the pressure in the compression chamber within thecylinder bore, and the pressure in the crank chamber, for variablycontrolling the discharge volume of the refrigerant gas.

A flow rate control valve mechanism is provided on a refrigerant supplypassage, which connects the discharge chamber to the crank chamber. Theflow rate control valve mechanism is provided with a discharge pressurechamber located on the discharge chamber side on the refrigerant supplypassage. An intermediate chamber is located on the crank chamber side onthe refrigerant supply passage. A valve hole is provided between thedischarge pressure chamber and the intermediate chamber to permit bothchambers to communicate with each other.

A pressure sensitive member is provided in the intermediate chamber toseparate the intermediate chamber into first and second pressuresensitive chambers. The first pressure sensitive chamber communicateswith the discharge pressure chamber via the valve hole. The secondpressure sensitive chamber communicates with the crank chamber or thesuction chamber.

The pressure sensitive member is displaceable as a function of thedifference between the pressures in the first and second pressuresensitive chambers. A restriction permits the first pressure sensitivechamber and the crank chamber to communicate with each other. A valvebody is coupled to the pressure sensitive member, and is displaceable insynchrony with the action of the pressure sensitive member. It changesthe amount of opening of the valve hole according to the displacement. Areturn member returns the valve body and the pressure sensitive memberto positions where the valve hole is opened by the valve body, when thepressure in the discharge chamber becomes almost zero.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. The invention,together with objects and advantages thereof, may best be understood byreference to the following description of the presently preferredembodiments together with the accompanying drawings in which:

FIG. 1 is a side cross-sectional view of a variable displacement swashplate type compressor according to a first embodiment of the presentinvention;

FIG. 2 is an enlarged cross-sectional view of a flow rate control valvemechanism for use in the compressor in FIG. 1;

FIG. 3 is a graph illustrating the relationship between the dischargepressure of the compressor in FIG. 1 and the pressure difference ininner and outer chambers of a bellows used in the flow rate controlvalve mechanism of FIG. 2;

FIG. 4 is a graph showing the relationship between the flow rate at arestriction of the compressor in FIG. 1 and the pressure difference inthe inner and outer chambers of the bellows of FIG. 3;

FIG. 5 is a graph illustrating the relationship between the dischargepressure of the compressor in FIG. 1 and the volume of refrigerantsupplied to the crank chamber;

FIG. 6 is an enlarged cross-sectional view of a flow rate control valvemechanism for use in a compressor according to a second embodiment ofthe present invention;

FIG. 7 is an enlarged cross-sectional view of a flow rate control valvemechanism for use in a compressor according to a third embodiment of thepresent invention;

FIG. 8 illustrates graphs showing the relationship between the dischargepressure of the compressor according to the third embodiment and thevolume of refrigerant supplied to the crank chamber, and therelationship between the flow rate at a restriction and the pressuredifference in the inner and outer chambers of the bellows;

FIGS. 9(a) to 9(d) are partial cut-away cross-sectional views ofcompressors according to modifications of the present invention;

FIG. 10 is a cross-sectional view of a flow rate control valve mechanismfor use in a compressor according to a further modification of thisinvention; and

FIG. 11 is a graph showing the relationship between the dischargepressure in a conventional compressor and the volume of refrigerantsupplied to the crank chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will now be describedreferring to FIGS. 1 through 5.

As shown in FIG. 1, a front housing 2 is connected to one end of acylinder block 1, while a rear housing 3 is connected via a valve plate4 to the other end of the cylinder block 1. A drive shaft 6 is disposedin a crank chamber 5 in the front housing 2, and is supported,rotatably, by radial bearings 7A and 7B.

A plurality of cylinder bores 8 (only one shown) are formed in thecylinder block 1 around the radial bearing 7B. Each cylinder bore 8communicates with the crank chamber 5. Pistons 9 are inserted into therespective cylinder bores 8 for defining a compression chamber 10between each piston 9 and the valve plate 4.

A drive plate 11 is rotatable in synchrony with the drive shaft 6, andis supported by the drive shaft 6 in the crank chamber 5. A sleeve 12 issupported slidably on the drive shaft 6. A spring 13 is disposed betweenthe drive plate 11 and the sleeve 12.

A rotary plate 15 is supported swingably on the sleeve 12 via a pair ofpins 14. The rotary plate 15 is ring shaped, and surrounds the driveshaft 6, with a bracket 15a projecting from part of the rotary plate 15.A support arm 11a protrudes from the drive plate 11, with an elongatedhole 16 formed therein. A guide pin 17 is attached to the distal end ofthe bracket 15a. In accordance with the engagement of the guide pin 17with the elongated hole 16 of the support arm 11a, the rotary plate 15rotates together with the drive shaft 6 and drive plate 11.

As the rotary plate 15 swings back and forth, the sleeve 12 slides backand forth on the drive shaft 6. The sliding of the sleeve 12 toward theradial bearing 7A is restricted when the spring 13 (shown in FIG. 1) iscompressed most. An inclined contact surface 11b is formed on the driveplate 11, such that, when the rotary plate 15 abuts the contact surface11b, and restricts the tilting of the rotary plate 15, the rotary plate15 comes to the most tilted position.

A swash plate 18 is mounted on the rotary plate 15 via a thrust bearing19. Like the rotary plate 15, the swash plate 18 is ring shaped, andsurrounds the drive shaft 6. The swash plate 18 is functionally coupledto the individual pistons 9 via a plurality of connection rods 20. Theswash plate 18 swings forward and backward interlockingly with therotation of the drive shaft 6 and the rotation of the tilted rotaryplate 15, while its rotation is inhibited by a rotation stop rod (notshown). In accordance with this swing action, each piston 9 reciprocatesin its associated cylinder bore 8.

A suction chamber 22 and a discharge chamber 23 are separated by apartition 21, and are formed in the rear housing 3. The valve plate 4 isprovided with a suction port 24 and a discharge port 25 in associationwith each cylinder bore 8. Each compression chamber 10 communicates withthe suction chamber 22 and the discharge chamber 23, through the suctionport 24 and discharge port 25. A suction valve 26 and a discharge valve27 are respectively provided in each suction port 24 and each dischargeport 25.

During the suction stage of the piston 9, the suction port 24 is openedby the suction valve 26, and the discharge port 25 is closed by thedischarge valve 27. During the discharge stage of the piston 9, thesuction port 24 is closed by the suction valve 26, and the dischargeport 25 is opened by the discharge valve 27. The suction chamber 22 anddischarge chamber 23 are provided with an inlet 28 and an outlet 29,respectively, through which the compressor of this embodiment isconnected, for example, to a refrigerating circuit (not shown) of arefrigerating apparatus.

As shown in FIG. 1, the cylinder block 1 is provided with a housing 30,and the valve plate 4 is provided with a communication hole 31 forallowing the housing 30 to communicate with the suction chamber 22. Acoupling 32 is fitted, via a seal ring 33, in the wall of the housing30, on the side of the crank chamber 5. A through hole 34 is bored inthe coupling 32 to permit the housing 30 to communicate with the crankchamber 5. A base 35 is fixed to the inner wall of the housing 30 on theside of the valve plate 4, with a plurality of through holes 36 bored inthe base 35.

A bellows 37 is secured on the base 35. Gas with predetermined pressureis sealed in this bellows 37, so that the bellows 37 expands andcontracts as a function of the pressure difference in the bellows 37 andthat in the housing 30. A needle valve 38 is mounted on the distal endof the bellows 37, so as to be engaged with, or disengaged from a valveseat 34a of the through hole 34, in accordance with the movement of thebellows 37. As the needle valve 38 is engaged with, or disengaged fromthe valve seat 34a, the crank chamber 5 communicates with the suctionchamber 22 through the through hole 34, housing 30, through hole 36 andcommunication hole 31, or is shut off from the chamber 22, forcontrolling the pressure in the crank chamber 5. As is apparent from theforegoing description, the coupling 32, bellows 37, and needle valve 38form a volume control valve mechanism 39.

As illustrated in FIGS. 1 and 2, a flow rate control valve mechanism 40is provided in the side wall of the rear housing 3. The flow ratecontrol valve mechanism 40 is provided with a discharge pressure chamber41, an intermediate chamber 42 and a crank-chamber pressure chamber(hereinafter simply referred to as crank pressure chamber) 43. Thedischarge pressure chamber 41 communicates with the discharge chamber 23via a communication opening 44. The crank pressure chamber 43communicates with the crank chamber 5 via a passage 45, which extendsthrough the rear housing 3 and the cylinder block 1.

A valve opening 46 is provided to allow the discharge pressure chamber41 to communicate with the intermediate chamber 42. A valve body 47 isloosely fitted in the valve hole 46 such that it is movable in theupward and downward directions. The valve body 47 has a head 47aretained in the discharge pressure chamber 41. The head 47a is engagedwith, or disengaged from a valve seat 46a at the upper periphery of thevalve hole 46. In accordance with this engagement or disengagement, thedischarge pressure chamber 41 communicates with the intermediate chamber42 or is fluidly disconnected from the chamber 42.

An elastic bellows 48 is retained in the intermediate chamber 42, andserves as a pressure sensitive member and a return member. The bellows48 has its bottom end secured to a partition 49 between the intermediatechamber 42 and the crank pressure chamber 43. The upper end of thebellows 48 is connected to the bottom end of the valve body 47, and iscovered by the valve body 47. The bellows 48 separates the intermediatechamber 42 into an outer chamber 42a (first pressure sensitive chamber)which communicates with the discharge pressure chamber 41, and an innerchamber 42b (second pressure sensitive chamber) which communicates withthe crank chamber 5. When the compressor is stopped, and the dischargepressure is zero, the valve body 47 is held at a position whichmaximizes the opening of the valve 46, as shown in FIG. 2, under theelastic force of the bellows 48.

A through hole 50 and a restriction 51 are formed through the partition49. The through hole 50 permits the inner chamber 42b to communicatewith the crank pressure chamber 43, while the restriction 51 allows theouter chamber 42a to communicate with the crank pressure chamber 43. Thethrough hole 50 therefore causes the refrigerant gas in the crankchamber 5 to enter the inner chamber 42b. The restriction 51 controlsthe flow rate of the compressed refrigerant gas flowing into the outerchamber 42a when the refrigerant gas is supplied via the crank pressurechamber 43 and passage 45, to the crank chamber 5.

According to the first embodiment, the through hole 44, the dischargepressure chamber 41, the valve hole 46, the inner chamber 42a, therestriction 51, the crank pressure chamber 43 and the passage 45constitute a refrigerant supply passage R which runs from the dischargechamber 23 to the crank chamber 5.

The flow rate control valve mechanism 40 of the first embodiment hascharacteristics as specified by graphs given in FIGS. 3 through 5. Inthe diagrams, Pd is the pressure in the discharge chamber 23 (dischargepressure), Ps is the pressure in the suction chamber 22 (suctionpressure), Pc is the pressure in the crank chamber 5 (crank chamberpressure), and Pw is the pressure in the outer chamber 42a (intermediatepressure).

The difference between the intermediate pressure Pw and the crankchamber pressure Pc, ΔP (ΔP=Pw-Pc), increases when the dischargepressure Pd is in a range from zero to predetermined discharge pressurePds, and it is maximum when Pd becomes Pds, as shown in FIG. 3. Thispredetermined discharge pressure Pds is previously determined in such away as to properly set the timing for the opening of the valve hole 46to start becoming smaller by the action of the valve body 47, anddepends on the elastic force of the bellows 48. In other words, theelastic force of the bellows 48 is determined to set the maximumdifference ΔPmax to the proper value. When the discharge pressure Pd isin a range from the predetermined discharge pressure Pds to criticaldischarge pressure Pd0 (the pressure at the time the valve hole 46 isclosed), the difference ΔP linearly decreases with an increase in thedischarge pressure Pd for the following reason. As the dischargepressure Pd increases, the intermediate pressure Pw increases. Theincreased intermediate pressure acts on the bellows 48 and the valvebody 47 to reduce the opening of the valve hole 46. When the opening ofthe valve hole 46 becomes smaller, the amount of refrigerant supply tothe outer chamber 42a from the discharge pressure chamber 41 decreases,thus reducing the amount of refrigerant discharge from the restriction51. Therefore, when the discharge pressure Pd is stable, the opening ofthe valve hole 46 is controlled, to keep the pressure difference ΔPnearly constant, by means of the valve body 47, as a function of thedifference between the intermediate pressure Pw and the crank chamberpressure Pc.

When the discharge pressure Pd becomes equal to, or greater than thecritical discharge pressure Pd0, the valve body 47 abuts the valve seat46a to completely block the valve hole 46. As a result, the differenceΔP between the intermediate pressure Pw and the crank chamber pressurePc becomes zero.

As shown in FIG. 4, the flow rate q, of the refrigerant passing throughthe restriction 51, and the above pressure difference ΔP, have such aproportional relation that as the pressure difference ΔP increases, therestriction flow rate q linearly increases. Given that ΔP1 and ΔP2 arethe pressure differences corresponding to discharge pressures Pd1 andPd2, and q1 and q2 are the restriction flow rates corresponding to Pd1and Pd2 in FIGS. 3 and 4, the relation of q1<q2 is established whenPd2<Pd1. As long as the discharge pressure Pd is in the range from thepredetermined discharge pressure Pds to the critical discharge pressurePd0, the higher the discharge pressure Pd is, the smaller therestriction flow rate q or the volume of refrigerant supply to the crankchamber 5 becomes.

In other words, the volume of refrigerant supply to the crank chamber 5via the flow rate control valve mechanism 40 increases in proportion toan increase in the discharge pressure Pd, when Pd ranges between zeroand the predetermined discharge pressure Pds, as indicated by a curve E1in FIG. 5. When the discharge pressure Pd lies in the range from thepredetermined discharge pressure Pds to the critical discharge pressurePd0, the volume of refrigerant supply linearly decreases; and when Pd isequal to or exceeds Pd0, the refrigerant supply to the crank chamber 5is stopped. The volume of the blow-by gas leaking to the crank chamber 5simply increases with an increase in the discharge pressure Pd, asindicated by a curve E2 in FIG. 5. As further indicated by a curve E1+2in FIG. 5, the sum of the volume of refrigerant supply by the flow ratecontrol valve mechanism 40 and the volume of refrigerant supply by theblow-by gas becomes stable between q1 and q2, while the dischargepressure Pd is in the range from the predetermined discharge pressurePds to the critical discharge pressure Pd0.

The proportional inclination in the relation between the restrictionflow rate q and the pressure difference ΔP is a function of the crankchamber pressure Pc. As indicated by the solid line and the broken linein FIG. 4, the greater the crank chamber pressure Pc is (expressed byPc2<Pc1), the lower the proportional inclination becomes. When the crankchamber pressure Pc varies, even if the pressure difference ΔP isconstant, the restriction flow rate q changes.

According to the first embodiment, as apparent from FIG. 5, therefrigerant gas is stably supplied to the crank chamber 5 within a givenpressure range, regadless of a change in the discharge pressure Pd.Unlike conventional devices, even when a load in the refrigeratingcircuit is low and the discharge pressure Pd is low, there will be asufficient volume of discharged gas supply to the crank chamber 5. It isthus possible to prevent the controllability of the discharge volumefrom dropping due to an insufficient volume of discharged gas. Even whenthe load in the refrigerating circuit is high and the discharge pressurePd is high, there will not be an oversupply of discharged gas to thecrank chamber 5. This can prevent the volume of discharged gas supply tothe refrigerating circuit from relatively decreasing, which otherwisereduces the refrigerating performance.

According to the first embodiment, when the drive shaft 6 stops rotatingto drop the discharge pressure Pd, the elastic force of the bellows 48displaces the valve body 47 in a direction to maximize the opening ofthe valve hole 46 in FIG. 2 (i.e., upward). Consequently, the compressedgas in the discharge chamber 23 flows into the crank chamber 5 via theflow rate control valve mechanism 40, rapidly making the crank chamberpressure Pc greater than the suction pressure Ps (Ps<Pc). At this time,this pressure increase together with the action of the spring 13 causethe sleeve 12 to promptly slide rightward (FIG. 1) so as to approach thecylinder block 1, therefore setting the inclination of the swash plate18 to the minimum angle. When this compressor is activated, thedischarge volume becomes minimum. This minimizes the torque load of thedrive shaft 6 so that the compressor can be activated smoothly.

Further, since the bellows 48 also serves as a pressure sensitive memberand a return member in this embodiment, the number of necessarycomponents can be reduced, for ensuring easier assembly.

A second embodiment of the present invention will now be describedreferring to FIG. 6.

In the second embodiment shown in FIG. 6, the inner chamber 42bcommunicates with the suction chamber 22 via a passage 52, to supply therefrigerant gas with suction pressure Ps into the inner chamber 42b. Thecompressor may be allowed to communicate with a suction pipe (not shown)of a refrigerating apparatus, via the passage 52. Likewise, thecompressor may be allowed to communicate with a discharge pipe (notshown) of the refrigerating apparatus, via the discharge pressurechamber 41.

In general, the suction pressure Ps changes less than the inner pressureof the crank chamber 5 (crank chamber pressure Pc). When the compressoris designed to allow the refrigerant gas with the suction pressure Ps toenter the inner chamber 42b as in the second embodiment, the pressuredifference ΔP' between the intermediate pressure Pw and the suctionpressure Ps, (ΔP'=Pw-Ps) becomes nearly constant. The crank chamberpressure Pc will not rise too much, making the flow rate q of therefrigerant gas through the restriction 51 stable.

A third embodiment of the present invention will now be describedreferring to FIGS. 7 and 8.

In the third embodiment, a cylindrical spool 53 with a cap is used forthe aforementioned bellows 48, and the valve body 47 is coupled to thatspool 53. Further, the spool 53 defines an outer chamber 42c and aninner chamber 42d. A coil spring 54 is provided in the inner chamber 42dfor urging the spool 53 together with the valve body 47, toward thereleasing position. In the top of the spool 53 is formed a restriction61 that allows the outer chamber 42c to communicate with the innerchamber 42d.

According to the third embodiment, the position of the spool 53 iscontrolled as a function of the pressure difference ΔP between theintermediate pressure Pw in the outer chamber 42c, and the crank chamberpressure Pc in the inner chamber 42d. In other words, while thedischarge pressure Pd rises from zero to the predetermined dischargepressure Pds, as shown in FIG. 8, after activation of the compressor,the spool 53 will not be displaced. The pressure difference ΔP thusrises linearly.

When the discharge pressure Pd reaches the predetermined dischargepressure Pds, the pressure difference ΔP reaches a maximum value. Whenthe discharge pressure Pd further rises, and the intermediate pressurePw increases accordingly, the valve body 47 shifts together with thespool 53 in a direction to reduce the opening of the valve hole 46,while compressing the spring 54. As a result, while the dischargepressure Pd rises beyond the predetermined discharge pressure Pds to thecritical discharge pressure Pd0, the pressure difference ΔP decreaseswith the increase in the discharge pressure Pd.

In the third embodiment, the pressure difference applied to the spool 53is expressed by the following equation, in which S1 denotes the entiresectional area of the valve hole 46, S2 denotes the pressure receivingarea of the spool 53 on the outer chamber (42c) side, and F is theelastic force of the spring 54:

    S1(Pd-Pw)+S2(Pw-Pc)=F

Rearranging the above equation yields the following equation for thepressure difference ΔP (=Pw-Pc) that acts on the spool 53.

    (Pw-Pc)=ΔP=F/S2-(Pd-Pw)S1/S2,

where Pw=(F+S1·Pc)/(S2-S1)-S1·Pd/(S2-S1).

As the pressure receiving area S2 of the spool 53 on the outer chamber(42c) side increases, the inclination of a graph indicated by a brokenline in FIG. 8 becomes lower.

Given that S3 denotes the sectional area of the restriction 61, the flowrate q of the refrigerant gas is calculated from the following equation:

    q=S3·√[(Pw-Pc)·Pc]

Thus, the flow rate q of the passing refrigerant gas is expressed by acurve shown in FIG. 8.

In this embodiment, to suppress the blow-by gas from the side clearancebetween the outer surface of the spool 53 and the inner wall of theintermediate chamber 42, the side clearance is made narrower foreffective action of the surface tension (viscosity) of a lubrication oilcontained in the refrigerant gas. In addition, the sectional area S3 ofthe restriction 61 is set sufficiently larger than the leak area of theside clearance. Further, the spool 53 functions in a range where thepressure difference ΔP acting on the spool 53 is low.

Since the urging force of the spring 54 can be set more properly thanthe elastic force of the bellows 48 in the third embodiment, it would berelatively easy to set the timing at which the opening of the valve hole46 starts becoming narrower by the valve body 47. This facilitates thegeneral designing of the flow rate control valve mechanism 40, andcontributes to cost reduction of the compressor. It should be noted thatthe other structures, functions and advantages of the third embodimentare similar to those of the first embodiment.

The present invention is not limited to the above-described embodiments,but may also be modified as follows.

(1) As shown in FIG. 9(a), the outer surface of the spool 53 may becoated with tetrafluoroethylene or like material to further narrow theside clearance. In this case, the lubricating action oftetrafluoroethylene smoothes the movement of the spool 53 to reduce thehysteresis of the flow rate of the refrigerant gas due to a change inthe discharge pressure.

Alternatively, a ring 56 having a rectangular cross section may befitted around the outer surface of the spool 53, as shown in FIG. 9(b),or an O-ring 56 may be fitted around outer surface of the spool 53, asshown in FIG. 9(c), to suppress the amount of the blow-by gas from theside clearance. Further, the restriction 61 of the spool 53 may beomitted while using the side clearance of the spool 53 itself as therestriction, as shown in FIG. 9(d).

(2) In the individual embodiments, the valve body 47 is fixed to thebellows 48 or the spool 53. As a modification to this structure, thevalve body and the spool may be formed of separate members, as shown inFIG. 10. More specifically, the valve body 47 comprises a ball valve 58,a holder 59 and a spring 60, with the ball valve 58 pressed against theend face of a support rod 53a of the spool 53 through the holder 59 bythe spring 60.

(3) As described above, the bellows 48 or the spool 53 is arranged belowthe valve body 47. As a modification to this structure, the verticalarrangement of the individual members 41, 43, 44, 46, 47 and 50 shown inFIG. 2 may be reversed. In this case, when the compressor is stopped,the valve body 47 is located under the force of gravity at a positionwhich provides maximum opening.

The present example and embodiment are to be considered as illustrativeand not restrictive, and the invention is not to be limited to thedetails given herein, but may be modified within the scope of theappended claims.

What is claimed is:
 1. A variable displacement swash plate typecompressor having a suction chamber, a discharge chamber and a crankchamber, the compressor comprising:flow rate control valve meansprovided along a refrigerant supply passage for connecting the dischargechamber to the crank chamber, said flow rate control valve meansincluding:a discharge pressure chamber located on the discharge chamberside along the refrigerant supply passage; an intermediate chamberlocated on the crank chamber side in the refrigerant supply passage; avalve hole provided between said discharge pressure chamber and saidintermediate chamber, to permit said discharge pressure chamber tocommunicate with said intermediate chamber; pressure sensitive meansprovided in said intermediate chamber for separating said intermediatechamber into a first pressure sensitive chamber, which communicates withsaid discharge pressure chamber via said valve hole, and a secondpressure sensitive chamber, which communicates with at least one of saidcrank chamber and said suction chamber, said pressure sensitive meansbeing displaceable as a function of a pressure difference between saidfirst and second pressure sensitive chambers; a restriction providedalong said refrigerant supply passage for permitting said first pressuresensitive chamber and said crank chamber to communicate with each other;a valve body connected to said pressure sensitive means, and beingdisplaceable in synchrony with the action of said pressure sensitivemeans, and being capable of regulating the opening of said valve holeaccording to that displacement; and a return member for returning saidvalve body and said pressure sensitive means to predetermined positionswhere said valve hole is opened by said valve body when pressure in saiddischarge chamber becomes almost zero.
 2. The compressor according toclaim 1, wherein said pressure sensitive means includes a bellowsmechanism, which surves as said return member.
 3. The compressoraccording to claim 1, wherein said pressure sensitive means includes acylindrical spool having a top portion, and wherein said first andsecond pressure sensitive chambers are defined by said top portion and awall of said spool.
 4. The compressor according to claim 3, wherein saidreturn member includes a spring for urging said spool toward said valvehole.
 5. The compressor according to claim 4, wherein said spring islocated in said wall of said spool.
 6. The compressor according to claim3, wherein a clearance is provided between an outer surface of said walland an inner wall of said intermediate chamber; wherein said top portionof said spool is provided with a restriction penetrating said topportion; and wherein said restriction has a section area that is largerthan said clearance.
 7. The compressor according to claim 6, whereinsaid outer surface of said wall is coated with tetrafluoroethylene. 8.The compressor according to claim 6, wherein a ring is secured to saidouter surface of said wall, for reducing said clearance between saidinner wall of said intermediate chamber and said outer surface of saidwall of said spool.
 9. The compressor according to claim 1, wherein saidvalve body is fixed to said pressure sensitive member.
 10. Thecompressor according to claim 1, wherein said valve body includes a rodprotruding from said pressure sensitive member and inserted into saidvalve hole, a ball valve capable of opening and closing said valve hole,and a spring for urging said ball valve in a direction for closing saidvalve hole.